Hip joint Osteoarthritis is a syndrome in which low-grade inflammation results in pain in the hip joints, caused by abnormal wearing of the Cartilage acting as a cushion inside if the hip joint. This abnormal wearing of the cartilage also results in a decrease of the joints lubricating fluid called Synovial fluid. Hip joint Osteoarthritis is estimated to affect 80% of all people over 65 years of age, in more or less serious forms.
The present treatment of hip joint osteoarthritis comprises NSAID drugs, local injections of Hyaluronic acid or Glucocorticoid to help lubricating the hip joint, and replacing parts of the hip joint with a prosthesis through hip joint surgery.
The replacing of parts of the hip joint is one of the most common surgeries to date performed on hundreds of thousand of patients in the world every year. The most common method comprises placing a metal prosthesis in Femur and a plastic bowl in Acetabulum. This operation is done through a lateral incision in the hip and upper thigh and through Fascia Lata and the lateral muscles of the thigh. To get access to the joint, the supporting hip joint capsule attached to Femur and Ilium needs to be penetrated. Femur is then cut at the neck with a bone saw and the prosthesis is placed in femur either with bone cement or without. Acetabulum is slightly enlarged using an Acetabular reamer, and the plastic bowl is positioned using screws or bone cement.
The metal prosthesis placed in femur is normally harder than the human bone which on many occasions injures the femoral bone in the points in which the prosthesis is fixated to the femoral bone. The difference in elasticity between the femoral bone and the hip joint prosthesis also affects the fixation of the prosthesis. Loosening of the prosthesis is the most common reason for needing to redo the hip joint surgery and a difference in elasticity between the prosthesis and the femoral bone creates tension in the fixation points which promotes the loosening of the prosthesis.
An additional problem with having a stiff i.e. not elastic enough prosthesis is that the prosthesis completely takes over the load carrying from the natural bone, which can make the bone retract and decreases its formation of new bone tissue. Eventually this process propagates loosening of the prosthesis. The strain on the contacting surfaces further comes from the shocks propagating through the body from normal walking or more extensive strains in accident situations such as the person falling. A stiff prosthesis does not work in a shock absorbing way and thus the entire shock is propagated to the contacting surface where the prosthesis is fixated to the femoral bone.
It would therefore be desirable to have a hip joint prosthesis with similar elastic properties as the bone in the points that fixates the prosthesis to the bone, and/or to have a hip joint prosthesis that absorbs shocks in a similar or improved way as the natural hip joint.